JP2016533929A - Method for applying image using UV curable phase change ink - Google Patents

Abstract

The present invention relates to a method of applying an image on a receiving medium using an ultraviolet curable phase change ink. The method comprises the steps of precuring the UV curable ink and post-curing the UV curable ink. The invention further relates to an ink jet apparatus configured to perform the above-described method.

Description

  The present invention relates to a method of applying an image using UV curable phase change ink and an ink jet printer suitable for carrying out such a method. Specifically, the present invention relates to an image coating method comprising two steps, a pre-curing step and a post-curing step, wherein the two curing steps are performed using a first ultraviolet beam and a second ultraviolet beam, respectively.

  Methods for applying images on recording media using UV curable inks are well known in the art. In general, such a method comprises applying UV curable ink onto a recording medium, for example, by ejecting ink droplets using an ink jet printer.

  After the ink is applied on the receiving medium, the ink is solidified by irradiating the ink with a suitable radiation source, preferably ultraviolet light. It is well known in the art that when the layer of UV curable ink applied on the receiving medium is relatively thick, it is not possible to properly cure the UV curable ink in one step. For example, the portion of the ink layer that is close to the receiving medium may not be fully cured. This problem may be solved by curing the ink in a two-step procedure, as described, for example, in US Patent Application Publication No. 2008/0174648. Therefore, it is known to irradiate UV curable ink with ultraviolet rays in order to properly cure the ink.

  However, irradiating a layer of ink applied on the receiving medium with one or more radiation sources can cause undesirable side effects, for example when UV curable phase change inks are used in the printing process. There is sex. UV curable phase change inks are fluid at high temperatures and may be solid or semi-solid at lower temperatures. This type of ink may be jetted as a fluid at high temperatures and cooled after it has been applied to the receiving medium, thereby changing it to a solid or semi-solid. If the temperature of the UV curable phase change ink applied on the record rises too much, the ink on the receiving medium may (partially) fluidize. This can cause printing artifacts. For example, the resulting printed gloss level after curing may be adversely affected. In addition, if the ink is fluidized before it is fully cured, ink adhesion can occur. Therefore, it is difficult to cure the layer of UV curable phase change ink so that the ink is fully cured without obtaining printing artifacts.

  Therefore, there is a need to apply images using UV curable phase change inks that alleviate the above problems.

US Patent Application Publication No. 2008/0174648

  The object of the present invention is therefore to provide such a method.

  Another object of the present invention is to provide an ink jet printer suitable for carrying out such a method.

This object is achieved in a method for applying an image on a receiving medium, the method comprising:
a) a step for injecting droplets of ink jet printing UV curable phase change ink from the head onto a receiver medium hot, high temperature is a temperature higher than the phase transition temperatures T _1, the phase transition temperatures T _1, it A step that is the temperature at which the ink becomes immobilized when:
b) the droplets of the deposited ink comprising the steps of cooling to a temperature lower than T _1, ink droplets are thereby changed from a liquid state to a stationary state, the steps,
c) precuring the deposited ink droplets by irradiating the ink droplets with a first ultraviolet beam, wherein the first beam has a first intensity;
d) post-curing the deposited ink by irradiating the ink droplets with a second ultraviolet beam, the second beam having a second intensity;
With
Pre-curing is done before post-curing,
The intensity of the first beam, at least before the curing step, the temperature of ink is controlled so as not to exceed T _1.

  In the method according to the invention, in step a), a droplet of ultraviolet (UV) curable phase change ink is applied to the receiving medium. For example, the droplets may be applied onto the receiving medium by ejecting the ink droplets using an inkjet device. The inkjet device may include a print head. The print head may include an orifice through which droplets of UV curable phase change ink are applied. The print head may further comprise a pressure chamber with a large amount of ink. The print head may further comprise actuation means for generating pressure in the fluid in the pressure chamber. Ink droplets may be ejected by pressure generated in the pressure chamber. The ink jet may further comprise an ink reservoir.

The ink used in the method according to the invention is a phase change ink. Phase change ink is ink that is liquid at high temperatures and immobilized at lower temperatures. For example, the phase change ink may be in a liquid phase at a temperature higher than the phase change temperature T _1. T ₁ may be, for example, 40 ° C., 60 ° C., 75 ° C., or 95 ° C. Such as a temperature below T _1, at lower temperatures, the phase change ink may be a different phase, i.e. immobilized state and liquid phase. In the liquid phase, also referred to as the fluid state, the ink composition can flow. For example, fluid ink may be ejected using an inkjet printhead. In addition, when liquid droplets of ink are applied onto the recording medium, the ink may flow over the surface of the recording medium. In this way, ink droplets can diffuse.

In the method according to the invention, in step b), the deposited ink droplets are cooled to a temperature below T ₁ , thereby changing the ink droplets from a liquid state to an immobilized state. Is less than the phase transition temperature T _1, ink may be in a fixed state. The fixed state is a state where ink cannot flow. In the immobilized state, the position and shape of the droplet may be substantially fixed. As a result, the droplet cannot diffuse onto the surface. Examples of immobilized states are solid and semi-solid. An example of a semi-solid phase is a gelled phase. In the ink reservoir and the pressure chamber, the ink may be a fluid state, therefore a temperature of at least T _1. In order to bring the ink to a temperature of at least T ₁ and to maintain the desired temperature, the ink jet apparatus may be provided with heating means for heating the ink. For example, the ink reservoir may be provided with heating means for heating the phase change ink. Alternatively or additionally, the pressure chamber may be provided with a heating means for heating the pressure chamber and the ink in the pressure chamber.

  The ink according to the present invention is a UV curable ink. UV curable inks are well known in the art. A UV curable ink is an ink comprising at least one UV curable component. The UV curing component can be cured when the ink is irradiated with ultraviolet rays. Ink curing is also known as ink solidification. The UV curable component may be, for example, a UV curable monomer and / or oligomer. Non-limiting examples of UV curable monomers are acrylate monomers, methacrylate monomers, and epoxy monomers. The monomer may be a monofunctional monomer (ie, a monomer comprising one radiation curable moiety) or the monomer may be a polyfunctional monomer (ie, a monomer comprising two or more radiation curable moieties).

  The UV curable ink composition may additionally comprise at least one photoinitiator for initiating curing (eg, initiating a polymerization reaction) upon curing of the ink composition. The UV curable ink composition may additionally comprise at least one inhibitor to prevent polymerization of the curable component of the ink, thereby extending the shelf life of the ink.

  The UV curable ink composition may further comprise a colorant. The colorant may be a pigment, a mixture of pigments, a dye, a mixture of dyes, a mixture of dyes and pigments, or a mixture of two or more dyes and two or more pigments. Pigments are preferred because of better color fixability than dyes.

The UV curable phase change ink composition may comprise at least one component that provides phase change properties to the ink composition. For example, the ink composition may comprise a component that solidify at a temperature lower than T _1. For example, the ink may comprise a meltable wax. Fusible waxes, at temperatures above T ₁ may be a liquid, it may be solidified at T _1. The meltable wax may be a reactive wax such as a radiation curable wax, or may be a non-reactive wax. The radiation curable wax may be a wax with a functional chemical group capable of undergoing a polymerization reaction upon exposure to radiation. The radiation curable wax may have, for example, an acrylate functional group or a methacrylate functional group.

  As a result of incorporating components that can solidify, a solidifying ink, or hot melt ink, is formed. Hot melt ink is an example of phase change ink. As the ink droplets solidify, the ink droplets become immobilized so that the droplets no longer flow, thus preventing droplet diffusion and smearing between the droplets.

In addition or alternatively, the ink composition may comprise a gelling agent. The ink provided with the gelling agent may be in a liquid phase above the gelling temperature of the gelling agent, or may be in a gelled state below the gelling temperature of the gelling agent. Gelling temperature of the gelling agent may be T _1. The gelled phase is the phase in which the gel exists as a dynamic equilibrium between the solid gelled material and the fluid. The gel phase is a dynamic network-like assembly of molecular components that are held together by non-covalent interactions. During the formation of the gelled phase, the viscosity of the ink composition may increase. The higher the viscosity, the higher the viscosity, which prevents the droplets from flowing, thereby immobilizing the droplets. For this reason, gelation of ink droplets can also prevent droplet diffusion and smearing between droplets.

  For this reason, both gelation and solidification are phase changes suitable for fixing the ink and preventing the diffusion of the droplets and smearing between the droplets. May be applied appropriately. In general, any phase change that weakens the fluidity of the ink droplets as the ink cools may be applied appropriately.

  The phase change properties of radiation curable inks allow the stabilization of the droplets applied on the receiving medium before being cured. For example, when phase change radiation curable ink is used to apply an image on a receiving medium, it need not be cured immediately after the droplets land on the receiving medium. There may be a time interval between the application and curing of the droplets on the receiving medium without causing droplet smearing.

  The radiation curable ink may be cured by irradiating the ink. The ink is emitted with a suitable radiation, for example ultraviolet light. Radiation induces a chemical reaction in the ink composition. For example, radiation can initiate a polymerization reaction of the ink, which causes the ink composition to solidify, thereby fixing the ink composition.

  In the method according to the invention, ink curing is performed in at least two steps. In the method, in step c), the deposited ink droplets are precured by irradiating the ink droplets with a first ultraviolet beam, the first beam having a first intensity. In the precuring step, radiation such as ultraviolet light may be provided by a suitable radiation source such as a lamp such as a UV lamp. The ultraviolet light source can generate a first ultraviolet beam. The first beam may have a first intensity. The intensity of the beam refers to the irradiance, ie the total amount of radiation locally received on the receiving medium per unit area.

  In the method, in step d), the deposited ink is post-cured by irradiating a droplet of ink with a second ultraviolet beam, the second beam having a second intensity. In the post-curing step, radiation such as ultraviolet light may be provided by a suitable radiation source such as a lamp such as a UV lamp. The ultraviolet source can generate a second ultraviolet beam. The second beam may have a second intensity. The intensity of the beam refers to the amount of energy applied by the beam on the receiving medium per unit area.

By performing pre-curing and post-curing, the image applied on the receiving medium can be properly cured. After the radiation curable phase change ink is cured, a network is formed in the ink and the radiation curable ink is no longer a fluid. After curing, the ink composition can no longer become fluid at a temperature T _1. Furthermore, by fixing the ink composition, the ink layer is firmly fixed to the receiving medium and is no longer easily removed from the receiving medium. The cured image may have a glossy appearance, a matte glossy appearance, or a semi-glossy appearance after curing.

  In the method according to the invention, the precuring takes place before the postcuring. Therefore, after the ink is applied on the recording medium, the ink is first precured and then postcured.

In the process according to the invention, the intensity of the first beam, at least before the curing step, the temperature of ink is controlled so as not to exceed T _1. The first ultraviolet beam may include ultraviolet rays having a plurality of wavelengths. The total amount of radiation causes heating of the ink when the ink is irradiated with the first beam. When the ink is heated, the temperature of the ink increases. For example, depending on the amount of heat supplied to the ink by the first beam of radiation, the temperature of the ink is likely to rise to a temperature higher than the phase change temperature T _1. In the precuring step, the ink is at most partially cured. The network formation between the polymerizable components present in the ink has not yet been completed, and unreacted polymerizable compounds may still be present. Therefore, when the temperature of the ink before the curing step is increased to a temperature higher than T _1, the ink (part of) is likely to return to a fluid state by receiving a phase change. Such a phase change can affect the gloss of the image. Therefore, the intensity of the first beam, at least before the curing step, the temperature of ink is controlled so as not to exceed T _1. Those skilled in the art will understand how the intensity of the beam can be properly controlled. For example, the amount of radiation emitted by the radiation source may be controlled. Alternatively, the source type may be appropriately selected. Alternatively or additionally, the distance between the ink deposited on the recording medium and the radiation source may be appropriately selected. In addition, suitable filters may be applied to reduce the intensity of radiation emitted by the source using a predetermined factor.

  When the ink is cured in the post-curing step, the ink is completely cured. When the ink is fully cured, i.e., basically all the polymerizable compounds are polymerized and the ink layer is solidified, heating of the ink layer no longer causes a partial phase change. For this reason, the second intensity, that is, the intensity of the second beam used in the post-curing step, may be higher than the first intensity of the first beam.

  In one embodiment, the first beam has a first dominant wavelength and the second beam has a second dominant wavelength. The first beam of radiation emitted by the first radiation source may emit a first spectrum of radiation, the spectrum having a certain width. The first spectrum can have a maximum value, i.e., a wavelength present in the beam of higher intensity than other wavelengths. This maximum value is referred to as the first dominant wavelength. Since the first dominant wavelength is emitted at a higher intensity compared to another wavelength present in the spectrum of the first beam radiation, the first dominant wavelength is compared to another wavelength in the curing process. It can have the strongest effect on it. The first dominant wavelength may be in the UV range, such as the UV-A range (410 nm to 315 nm), the UV-B range (315 nm to 280 nm), or the UV-C range (280 nm to 100 nm). The second beam of radiation emitted by the second radiation source may reflect a second spectrum of radiation, the spectrum having a certain width. The second spectrum can oscillate the maximum value, ie the wavelength present in the beam of higher intensity than the other wavelengths. This maximum value is referred to as the second dominant wavelength. The second dominant wavelength is emitted at a higher intensity compared to another wavelength present in the spectrum of the radiation of the second beam, so the second dominant wavelength is another wavelength emitted by the second radiation source. As compared to the curing process. The second dominant wavelength may be in the UV range, such as the UV-A range (410 nm to 315 nm), the UV-B range (315 nm to 280 nm), or the UV-C range (280 nm to 100 nm).

  Further, in the embodiment, the first dominant wavelength is different from the second dominant wavelength. The radiation of the first beam may have a dominant wavelength that is different from the dominant wavelength of the second ultraviolet beam. The ink composition may comprise a number of components, some of which can absorb ultraviolet radiation, such as radiation at the first dominant wavelength and / or radiation at the second dominant wavelength. When ultraviolet light is absorbed by UV curable monomers or oligomers or by photoinitiators present in the ink composition, this can result in polymerization of the curable polymers and / or oligomers, and thus the ink can be cured. However, other components in the ink, such as pigments, can also absorb ultraviolet light. UV absorption by the pigment cannot cause ink curing. When components such as pigments are present in the ink composition that absorbs ultraviolet radiation emitted by the first beam of radiation, curing is slow in the portion of the ink layer close to the receiving medium (under the ink layer). It may be early at the top of the ink layer. Therefore, the ink layer may not be properly cured. Thus, in the method according to the invention, the precuring step is performed using a first ultraviolet beam. The first dominant wavelength penetrates deeply into the ink layer and can also cure the interior of the ink layer. The first curing step can induce a slow curing of the ink layer. In other words, some of the polymerizable portions in the ink may polymerize during the precuring step. However, the ink layer cannot be fully cured during the precuring step. Partial curing can further fix the ink. After the pre-curing step, the ink is cured in the post-curing step using UV light having a second wavelength, which is different from the first wavelength. This second ultraviolet light does not need to penetrate the ink layer, but only cures the upper part of the ink layer. However, the second curing step can induce faster curing than the first curing step. In addition, the top of the layer can be in contact with oxygen in the air. The presence of oxygen can interfere with the curing process, so post-curing may provide at least additional radiation to the upper layer in order to properly cure the upper layer of the print.

  The first and second dominant wavelengths are appropriately selected based on the absorption spectra of other components present in the ink, such as, for example, the photoinitiator, the polymerizable compound (s), and the pigment. May be.

  By applying pre-curing and post-curing tapes, the ink layer is fully cured so that a thick layer of ink can be cured in a two-step curing process.

  In a further embodiment, the first dominant wavelength is longer than the second dominant wavelength. Radiation having longer wavelengths is less effectively absorbed by components in the ink that do not polymerize upon curing, such as pigments. Thus, longer wavelengths penetrate deeper into the ink layer and can therefore be applied appropriately to pre-curing the ink layer.

In one embodiment, the ink comprises a gelling material. Radiation curable gel ink composition may be a fluid at a temperature higher than T _1. In temperatures T ₁ below, the gelling agent forms a gel, by forming a gel, the gelling agent can be gelled ink. The ink then becomes a so-called gelled phase. Thus, the gelling agent, when cooling the ink composition to a temperature lower than T _1, to provide a phase change in the ink.

  As explained above, the gelled phase may be viewed as a phase in which there is a dynamic equilibrium between the solid gelled material and the fluid. The gel phase is a dynamic network-like assembly of molecular components that are held together by non-covalent interactions. A networked assembly of molecular components can be formed by a gelling agent. The fluid present in the network assembly formed by the gelling agent may comprise a radiation curable component. In addition, the fluid may comprise additional ink components, such as photoinitiators, inhibitors, and / or colorants. Thus, when the droplets are converted from fluid to gel and consequently prevented from spreading, the radiation curable component may still be in the fluid phase. While not wishing to be bound by any logic, the curing of the ink that can be achieved by inducing a polymerization reaction to polymerize the radiation curable component is compared to the situation where the radiation curable component is in the solid state. Thus, it is believed that this occurs faster when the radiation curable component is in the fluid state.

  The gelling agent may be appropriately selected. The gelling agent may be a component capable of forming a (super) molecular network.

Non-limiting examples of many gelling agents are: ketones such as: laurone, stearone, di-n-dodecyl ketone, pyriston, 15-nonacosanone, behenone, palmitone, di-n-hexadecyl ketone; An oligoester compound is a reaction product of a polyhydroxy component such as pentaerythritol or glycerol with a carboxylic acid having an alkyl chain such as stearic acid, palmitic acid, arachidic acid, linoleic acid, or myristic acid ester. ester _compounds; and C 20 _{-C 25} long-chain terminal alcohols, such as _{C 10-C40} long-chain terminal alcohols such as _C 15 _{-C 30} long-chain terminal alcohol is a long chain terminal alcohol. Examples of commercially available long chain terminal alcohols are available from Baker Hughes Inc. More available Unilin® wax. Additional non-limiting examples of gelling agents can be found in Baker Hughes Inc. Long chain terminal carboxylic acid waxes such as UNICID® wax commercially available; Urfe American Dye Source Inc., Baie D ', Quebec, Canada. Urethane waxes such as ADS043 or ADS039 commercially available; waxes of natural origin such as candelilla wax, celilla wax, montan wax; alkyl ester waxes such as Kester Wax K-AE-80 commercially available from Koster Keunen; Amide waxes such as primary amide waxes or secondary amide waxes, such as amide waxes, stearyl stearate, erucamide; or reactive waxes. Non-limiting examples of reactive waxes are acrylate waxes such as alkyl acrylate waxes, vinyl ether waxes, and alkene waxes such as oleyl arachidate. Examples of commercially available reactive waxes are Clariant International Ltd. More available are reactive Licomont (R) wax and reactive Ceridust (R) wax.

In one embodiment, the ink comprises a crystalline component and T ₁ is the melting temperature of the crystalline component.

When the ink is ejected, the ink is in a fluid state, the temperature of the ink is therefore a temperature higher than T _1. At such a temperature, the crystalline component having a melting temperature of T ₁ is in a fluid state. When ink is ejected onto the recording medium, the ink droplets are cooled to a temperature below T1. When cooled, the crystalline component solidifies and crystallizes. The rate of crystallization is affected by the ink cooling rate, which can be controlled, for example, by controlling the temperature of the media. Crystals are formed when the crystalline components present in the ink composition crystallize. Crystals affect the gloss of the image applied on the receiving medium.

During the precuring step, the layer of ink may be cured at most or only partially. Both the portion of the ink layer that is close to the receiving medium and the top of the ink layer (ie, the portion of the ink layer that is far from the receiving medium) are only partially cured at most. When the ink layer is at least partially cured, the network formation between the cured components of the ink is not yet complete. During the precuring step, the ink is partially cured by irradiating the ink with a first beam of radiation. This beam has a first intensity, so that the ink is heated by the irradiation of the first beam. Before the curing step, the intensity of the first beam, the temperature of ink is controlled so as not to exceed T _1. As a result, the crystalline component having the melting temperature T ₁ does not melt and remains in crystalline form. While not wishing to be bound by any logic, it is believed that melting of crystalline material in an ink layer that has not yet fully cured can irreversibly change the gloss properties of the print. Thus, by the temperature of the ink to control the intensity of the first beam so as not to exceed T _1, it is possible to gloss properties of print is held.

In the post-curing step, the ink layer may be further cured. Thus, the ink may be cured to the extent that a robust layer with a network of cured ink components is formed. Post-curing may be performed by irradiating the ink with a second beam of radiation, the second beam having a second intensity. While not wishing to be bound by any logic, it is believed that once a robust layer is formed, the fluidity of the ink components in the ink layer is very low. When the temperature of the cured layer exceeds T _1, which can not at all or little effect on print gloss.

  Optionally, the crystalline component may be a gelling material. When the gelling material is a crystalline component, the gelling material can provide both a phase change characteristic for and an effect on the gloss of the print. Alternatively, the crystalline component may be another component of the ink composition, such as a binder.

Non-limiting examples of crystalline gelling agents include ketones such as laurone, stearone, di-n-dodecyl ketone, pyriston, 15-nonacosanone, palmitone, di-n-hexadecyl ketone; C ₂₀ -C ₂₅ long chain terminal alcohols Such as C ₁₅ -C ₃₀ long chain terminal alcohols such as C ₁₀ -C ₄₀ long chain terminal alcohols; long chain terminal alcohols; or urethane waxes such as commercially available Vectoromer® monomers available from Sigma-Aldrich Vinyl ether wax.

  Optionally, more than one crystalline gelling agent may be used in the ink composition. Optionally, in an ink set comprising a plurality of ink compositions, such as an ink set comprising cyan, magenta, yellow, and black inks, the crystalline gelling agent contained in each of the respective ink compositions in the ink set The type and amount may vary.

  In one embodiment, in step a), the print head reciprocates in the main scanning direction, which is substantially perpendicular to the paper transport direction.

  In inkjet scanning, the print head and the receiving medium that eject droplets may move in the main scanning direction relative to each other. This may be done by moving the print head mounted on the carriage in the main scanning direction over the receiving medium when applying ink drops to the receiving medium.

  In current swaths, the carriage carrying the printhead and the receiving medium move relative to each other, and a pattern of droplets can be printed on the receiving medium, thereby forming (part of) an image. After the current swath is complete, the carriage and receiving medium may be moved relative to each other in a paper transport direction, also known as the sub-scanning direction. The relative movement of the carriage and receiving medium relative to each other between the swaths is known as a paper step. The receiving medium is positioned such that a portion of the receiving medium not yet provided with an image is positioned so that the print head ejects ink droplets onto that portion of the receiving medium as the carriage moves in the main scanning direction. Moved. Preferably, the movement in the sub-scanning direction prevents the paper step from being visible in the printed image.

  After the paper step is performed, the carriage and receiving medium are moved again in the main scanning direction in the next swath relative to each other.

  In a further embodiment, step c) provides a first UV beam by a first UV source, step d) provides a second UV beam by a second UV source, and the first UV source and the second UV source are either Are also moved in the main scanning direction synchronously.

  The print head (s) and UV source may be reciprocated in the main scanning direction. The print head (s) is positioned at a distance from the ultraviolet light source in the paper transport direction. In the context of the present invention, the synchronous movement of the print head and the UV source means that the print head and the UV source start and stop simultaneously in the main scanning direction. The moving speeds of the print head and the ultraviolet light source in the main scanning direction are preferably the same. Preferably, the width of the swath printed by the print head corresponds to the width of the image illuminated by the first UV source.

  The print head and UV source may move synchronously in the same direction. Alternatively, the print head and UV source may move synchronously in opposite directions. By moving the print head and UV source synchronously, the time between ink ejection onto the receiving medium and ink curing is constant. As a result, the degree to which the ink is cooled is constant. Therefore, the characteristics of the ink droplets are constant, and the appearance of the ink after curing is also constant.

If the ink comprises a crystalline component having a melting temperature T _1, the degree of crystal components form a crystal is constant. This can prevent uneven gloss across the printed image after curing.

In an aspect of the invention, an inkjet printer for applying an image on a receiving medium is provided, the inkjet printer comprising:
An inkjet printhead configured to eject droplets of ultraviolet curable phase change ink;
A first UV source adapted to provide a first UV beam during operation;
A second UV source adapted to provide a second UV beam during operation;
Transport means for moving the recording medium in the paper transport direction relative to the inkjet print head and the first and second ultraviolet light sources;
With
The second ultraviolet light source is positioned downstream with respect to the ink jet print head and the first ultraviolet light source.

  The ink jet device according to the invention is thus configured to carry out the method according to the invention.

  The first ultraviolet light source may be a lamp such as a mercury lamp, a xenon lamp, a carbon arc lamp, a tungsten bulb, a light emitting diode (LED), and a laser. The first ultraviolet source emits a first beam having a first intensity. The intensity of the beam is controlled by the amount of energy supplied to the first ultraviolet source, and by selecting an appropriate radiation source, the first radiation having a filter that reduces the intensity of the first beam to a predetermined intensity. It may be controlled by providing a source. In addition, the intensity of the beam that irradiates the ink applied on the receiving medium may be appropriately controlled by controlling the distance between the receiving medium and the radiation source. In one embodiment, the first source can emit a first spectrum having a first dominant wavelength.

  The second radiation source may be a lamp such as a mercury lamp, a xenon lamp, a carbon arc lamp, a tungsten bulb, a light emitting diode (LED), and a laser. The second ultraviolet light source emits a second beam having a second intensity. The intensity of the beam may be controlled as described for the first UV source. In one embodiment, the second source can emit a second spectrum having a second dominant wavelength.

  The first beam of radiation and the second beam of radiation may be provided by two different lamps. Alternatively, the radiation source may be a lamp and filter assembly, where the lamp emits first and second dominant wavelengths and the lamp is provided with two different filters; one filter is of first intensity radiation And the second filter transmits radiation of the second intensity. In one embodiment, one filter can transmit a first spectrum of ultraviolet light having a first dominant wavelength, and a second filter can transmit a second spectrum having a second dominant wavelength.

  Preferably, both the first dominant wavelength and the second dominant wavelength are in the UV-A range, which comprises radiation having a wavelength in the range of 320 nm to 410 nm.

  Preferably, the first dominant wavelength is 410 nm to 250 nm, preferably 408 nm to 320 nm, such as 405 nm to 360 nm, such as 400 nm to 380 nm. Preferably, the second dominant wavelength is 405 nm to 210 nm, preferably 403 nm to 300 nm, such as 400 nm to 350 nm, such as 395 nm to 375 nm.

First ^{strength, 0.1W / cm 2 ~30W / cm} 2, for example, ^{0.3W / cm 2 ~20W / cm 2} , may be in the range such 0.5W / cm ² ~10W / cm 2 .

Second intensity ^may be in the range such ^{0.5W / cm 2 ~40W / cm 2} , for example, ^{1.0W / cm 2 ~25W / cm 2} , 5W / cm 2 ~15W / cm 2.

  The second strength may be 1.2 to 10 times higher than the first strength. Preferably, the second strength may be 1.5 to 7 times as high as the first strength. For example, the second strength may be 2-5 times higher, such as 3-4 times the first strength.

  In one embodiment, the ink jet printer may comprise temperature adjusting means for adjusting the temperature of the receiving medium.

  In step b) of the method according to the invention, the ink deposited on the receiving medium is cooled. The cooling rate may depend on a number of parameters such as the jetting temperature of the ink, the amount of ink applied on the receiving medium, the ambient temperature, and / or the temperature of the receiving medium. The ink temperature at the moment when the ink is precured may depend, for example, on the ink cooling rate in step b). The temperature of the ink applied on the receiving medium may be appropriately controlled by controlling the temperature of the receiving medium on which the ink droplets are applied. The temperature of the receiving medium may be controlled by suitable temperature adjusting means. The temperature adjusting means may be configured to cool the receiving medium and / or to heat the receiving medium. Any suitable type of temperature adjustment means may be used. For example, electric heating or cooling may be used. Optionally, a cooling fluid such as water may be used.

  These and other features and advantages of the present invention are described below with reference to the accompanying drawings, which illustrate non-limiting embodiments.

1 is a schematic diagram of an inkjet printing system. It is the schematic of an inkjet print head. 1 schematically shows a first embodiment of the method according to the invention. FIG. FIG. 3 schematically shows a second embodiment of the method according to the invention. FIG. 3 schematically shows a third embodiment of the method according to the invention. FIG. 6 schematically shows a fourth embodiment of the method according to the invention. FIG. 6 schematically shows a fourth embodiment of the method according to the invention.

  In the figures, like reference numerals refer to like elements.

  FIG. 1A shows an inkjet printing assembly 3. The ink jet printing assembly 3 comprises support means for supporting the image receiving medium 2. The support means is shown as plane 1 in FIG. 1A, but alternatively the support means may be a platen, such as a rotating drum rotatable about an axis. The support means may be selectively provided with a suction hole for holding the image receiving medium at a fixed position with respect to the support means. The inkjet printing assembly 3 includes print heads 4 a to 4 d mounted on a scanning print carriage 5. The scanning print carriage 5 is guided by appropriate guide means 6 so as to reciprocate in the main scanning direction X. Each print head 4a-4d includes an orifice surface 9, which is provided with at least one orifice 8, as shown in FIG. 1B. The print heads 4 a to 4 d are configured to eject drops of marking material onto the image receiving medium 2.

  The image receiving medium 2 may be a web or sheet-like medium, and may be made of, for example, paper, cardboard, label material, coated paper, plastic, or cloth. Alternatively, the image receiving medium 2 may also be an intermediate member that may or may not be endless. Examples of endless members that can move cyclically are belts or drums. The image receiving medium 2 is moved in the sub-scanning direction Y over the plane 1 along the four print heads 4a-4d provided with the fluid marking material.

  The image receiving medium 2 as shown in FIG. 1A is locally heated or cooled in the temperature control region 2a. In order to control the temperature of the receiving medium 2 in the temperature control region 2a, temperature control means (not shown) such as heating and / or cooling means may be provided. Optionally, the temperature control means may be incorporated in a support means for supporting the image receiving medium 2. The temperature control means may be an electrical temperature control means. The temperature control means may use a cooling liquid and / or a heating liquid in order to control the temperature of the image receiving medium 2. The temperature control means may further comprise a sensor (not shown) for monitoring the temperature of the image receiving medium 2.

  The scanning print carriage 5 carries four print heads 4 a to 4 d and is reciprocated in the main scanning direction X parallel to the platen 1 in order to enable the operation of the image receiving medium 2 in the main scanning direction X, for example. May be. In order to demonstrate the present invention, only four print heads 4a-4d are shown. In practice, any number of print heads may be employed. In any case, at least one print head 4 a-4 d is arranged on the scanning print carriage 5 for each color of the marking material. For example, in a black and white printer, there is usually at least one print head 4a-4d that contains black marking material. Alternatively, the black and white printer may comprise a white marking material that is applied onto the black image receiving medium 2. In a color printer that includes many colors, there is typically at least one print head 4a-4d for each color of black, cyan, magenta, and yellow. Often, in color printers, black marking materials are used more frequently compared to marking materials of different colors. Accordingly, the print heads 4a to 4d including the black marking material may be provided more on the scanning print carriage 5 than the print heads 4a to 4d including the marking material of any other color. . Alternatively, the print heads 4a-4d that include black marking material may be larger than any of the print heads 4a-4d that include marking materials of different colors.

  The carriage 5 is guided by the guide means 6. These guiding means 6 may be rods as shown in FIG. 1A. Although only one rod 6 is shown in FIG. 1A, a plurality of rods may be used to guide the carriage 5 carrying the print head 4. The rod may be driven by suitable drive means (not shown). Alternatively, the carriage 5 may be guided by another guiding means such as an arm that can move the carriage 5. Another alternative is to move the image receiving material 2 in the main scanning direction X.

  Each print head 4a-4d includes an orifice surface 9 having at least one orifice 8 in fluid communication with a pressure chamber containing fluid marking material provided on the print heads 4a-4d. On the orifice surface 9, as shown in FIG. 1B, a large number of orifices 8 are arranged in a single linear linear array parallel to the sub-scanning direction Y. Alternatively, the nozzles may be arranged in the main scanning direction X. Eight orifices 8 are shown in FIG. 1B for each printhead 4a-4d, but as is apparent in the actual embodiment, hundreds of orifices 8 are selectively selected for each printhead 4a-4d. It may be arranged in a plurality of arrangements.

  As shown in FIG. 1A, the respective print heads 4a to 4d are arranged parallel to each other. The print heads 4a to 4d may be arranged so that the corresponding orifices 8 of the respective print heads 4a to 4d are positioned in a straight line in the main scanning direction X. This means that a row of image dots in the main scanning direction X is formed by selectively activating up to four orifices 8, each of which is part of a different print head 4a-4d. This parallel arrangement of printheads 4a-4d with a corresponding linear arrangement of orifices 8 is advantageous for improving productivity and / or improving print quality. Alternatively, the plurality of print heads 4a-4d may be arranged on the print carriage adjacent to each other so that the orifices 8 of the respective print heads 4a-4d are positioned in a zigzag configuration rather than in a straight line. For example, this may be done to increase the print resolution or to enlarge the effective print area, which is accommodated with a single scan in the main scan direction X. The image dots are formed by ejecting a droplet of marking material from the orifice 8.

  The inkjet printing assembly 3 may further include curing means 11a and 11b. As shown in FIG. 1A, the scanning print carriage 12 carries two curing means 11a, 11b and enables the scanning of the image receiving medium 2 in the main scanning direction X, etc. It may be reciprocated in the parallel main scanning direction X. Alternatively, three or more curing means may be applied. When a page width curing unit that can also apply a page width curing unit is provided, it is not necessary to reciprocate the curing unit in the main scanning direction X. The first curing means 11a may emit a first ultraviolet beam, and the first beam has a first intensity. The first curing means 11a is configured to provide radiation for the precuring step. The second curing means 11b may emit a second beam of radiation, the second beam of radiation having a second intensity. The second curing means 11b is configured to provide radiation for the post-curing step.

  The carriage 12 is guided by the guide means 7. These guiding means 7 may be rods as shown in FIG. 1A. Although only one rod 7 is shown in FIG. 1A, a plurality of rods may be used to guide the carriage 12 carrying the print head 11. The rod 7 may be driven by suitable drive means (not shown). Alternatively, the carriage 12 may be guided by another guiding means such as an arm that can move the carriage 12.

  The curing means may be an actinic radiation source, an accelerated particle source, or an energy source such as a heater. Examples of actinic radiation sources are ultraviolet light sources or visible light sources. Ultraviolet sources are preferred because they are particularly suitable for curing such inks by inducing polymerization reactions in UV curable inks. Examples of suitable sources of such radiation are lamps such as mercury lamps, xenon lamps, carbon arc lamps, tungsten bulbs, light emitting diodes (LEDs), and lasers. In the embodiment shown in FIG. 1A, the first curing means 11a and the second curing means 11b are positioned parallel to each other in the sub-scanning direction Y. The first curing means 11a and the second curing means 11b may be the same type of energy source or different types of energy sources. For example, when both the first and second curing means 11a, 11b both emit actinic radiation, the wavelengths of radiation emitted by the two curing means 11a, 11b may be different or the same. Also good. The first and second curing means are depicted as separate devices. Instead, however, only one UV source that emits a spectrum of radiation may be used with at least two different filters. Each filter absorbs a portion of the spectrum, thereby providing two beams of radiation, each having a different intensity.

  The plane 1, temperature control means, carriage 5, print heads 4a to 4d, carriage 12, and first and second curing means 11a, 11b are controlled by suitable control means 10.

FIG. 2 schematically shows a first embodiment of the method according to the invention. A print head 4 is provided that is configured to eject ink droplets 15 onto the receiving medium 2. Although only one printhead 4 is shown in FIG. 2, in practice multiple printheads may be provided, selectively ejecting different colors of ink. Each of the droplets 15 is in a fluid state when ejected by the print head. In order to keep the ink in a fluid state, the print head may be provided with heating means (not shown). The ink may begin to cool after being ejected from the print head 4 through nozzles (not shown). Due to the cooling of the ink, the ink may undergo a phase change. The receiving medium 2 on which the ink droplets 15 are applied is moved in the direction Y which is the paper transport direction. When a scanning inkjet process is used, such as that shown in FIG. 1, for example, the paper transport direction is often referred to as the main scanning direction. After the ink droplets are applied, the droplets may continue to cool, and a phase change may occur, which results in the formation of immobilized droplets 16. The fixed droplets 16 are transported in the paper transport direction Y together with the receiving medium. Thereby, the immobilized droplet 16 is moved under the first ultraviolet ray source 11a. The first ultraviolet source 11 a emits a first beam of radiation, schematically shown as a ray of radiation 21. The radiation emitted by the first radiation source 11a may have a first intensity. The immobilized droplets are precured by the radiation beam 21 emitted by the first radiation source 11a. The intensity of the radiation, the temperature of the droplet 16 is selected so as not to exceed T _1. Therefore, the droplet remains in an immobilized state. By precuring the droplets, the immobilized droplets 16 can partially cure and thereby be further immobilized. There may be a specific time interval after the post-curing until the droplet is post-cured. Since the droplet 16 is fixed, this does not adversely affect the quality of the image formed.

After the immobilized droplet 16 is precured, the droplet is moved under the second ultraviolet light source 11b. This second ultraviolet source 11b emits a second beam of radiation, schematically shown as a ray of radiation 22. The radiation emitted by the second source 11b may have a second intensity. The immobilized droplets are post-cured by the radiation beam 22 emitted by the second radiation source 11b. When the droplet 16 is post-cured, the droplets are fixed on the receiving medium, be heated even to a temperature higher than T _1, it does not cause longer change shape.

  The types of the first radiation source 11a and the second radiation source 11b can be appropriately selected.

  FIG. 3 schematically shows a second embodiment of the method according to the invention. The second embodiment differs from the first embodiment in the relative positioning of the first and second radiation sources 11a and 11b.

  The distance between the first radiation source 11a and the receiving medium 2 is longer than the distance between the second radiation source 11b and the receiving medium 2. As in the embodiment shown in FIG. 2, the first radiation source 11a emits a first type of radiation having a first spectrum, the first spectrum having a first dominant wavelength. The radiation emitted by the first radiation source 11a has a first intensity. The second radiation source 11b emits a second type of radiation, the second type of radiation having a second spectrum, the second spectrum having a second dominant wavelength. The radiation emitted by the second radiation source 11b has a second intensity.

  The beam of radiation emitted by the first radiation source 11a, schematically shown as the first radiation ray 21, is divergent. As a result, the diameter of the beam emitted by the first radiation source 11a increases as the distance from the first radiation source 11a increases. Therefore, the intensity of the beam that locally irradiates the droplet 16 decreases as the distance between the droplet and the radiation source 11a increases. As a result, the intensity of the beam that irradiates the immobilized droplet 16 and thereby pre-cures the immobilized droplet applied on the receiving medium 2 is such that the intensity of the beam between the receiving medium 2 and the first radiation source 11a. It can be controlled by controlling the distance between them.

  FIG. 4 schematically shows a third embodiment of the method according to the invention. The third embodiment differs from the first and second embodiments in the nature of the first and second radiation sources. The radiation source according to the third embodiment is an assembly of an ultraviolet general source 11 and a filter. A first filter 11c and a second filter 11d are provided. The first and second filters 11c and 11d may be optical filters, for example. Each of the filters 11c and 11d absorbs part of the radiation emitted by the general ultraviolet ray source 11 and transmits part of the ultraviolet radiation emitted by the general ultraviolet ray source 11. Part of the beam of radiation, schematically shown as radiation beam 20, emitted by the ultraviolet general source 11 is transmitted through the first filter 11c and another part of the beam is transmitted through the second filter 11d. . The portion of the beam that passes through the first filter 11c provides a first beam of radiation, shown schematically as a ray 21 of radiation. The radiation in the first beam of radiation has a first spectrum, and the first spectrum has a first dominant wavelength. Radiation emitted by the general radiation source 11 that is not included in the first spectrum of the first beam may be absorbed by the first filter 11c.

  A second filter 11d is provided next to the first filter 11c. The portion of the beam emitted by the general radiation source 11 that is transmitted through the second filter 11d provides a second beam of radiation, shown schematically as a ray 22 of radiation. The radiation in the second beam of radiation has a second spectrum, and the second spectrum has a second dominant wavelength.

  For this reason, the first filter 11c and the second filter 11d each absorb a part of the radiation emitted by the general radiation source 11 and generate two different beams of radiation, each beam having a dominant wavelength. Good. The first filter 11c is provided upstream in the paper transport direction compared to the second filter 11d. Thus, the ink droplets applied and fixed on the receiving medium 2 first pass under the first filter 11c and are thereby irradiated by the first beam of radiation. The first beam of radiation induces precuring of the immobilized droplet 16. Thereafter, the precured droplet passes under the second filter 11d and is then irradiated by a second beam of radiation. The second beam of radiation can induce post-curing of the ink droplet 16.

  Therefore, in the present embodiment, the first radiation source and the second radiation source are appropriately realized by providing the general radiation source 11 and the first and second filters 11c and 11d.

  FIG. 5A schematically shows a fourth embodiment of the method according to the invention. A first radiation source 11a as well as a second radiation source 11b are also provided. The first beam 21a of radiation emitted by the first radiation source 11a is divergent, i.e. the diameter of the beam expands with increasing distance from the radiation source 11a. The second beam 22a emitted by the second radiation source is also diverging. The first beam 21a and the second beam 22a irradiate the receiving medium and the immobilized droplet 16 deposited thereon. When the immobilized droplets 16 are moved in the paper transport direction, they are first irradiated at the point A by the first beam 21a. Therefore, at point A, pre-curing of the immobilized droplet 16 can be started. When the droplets 16 applied on the receiving medium are further moved in the paper transport direction, they are first irradiated at point B by a second beam of radiation 22a. Thus, when the ink droplet 16 passes point B, post-curing of the droplet can begin. The ink droplet 16 is irradiated by the second beam 22 a until it passes through the point C.

  For clarity, the first and second beams of radiation 21a, 22a are depicted away from the receiving medium. In practice, however, the first and second beams 21a, 22a irradiate the receiving medium 2 and the droplets 16 deposited thereon.

The intensity of the beam at the surface of the receiving medium 2 is not uniform. The intensity of the radiation provided by the first radiation source 11a is the strongest immediately below the radiation source 11a, and decreases as the position moves away from the radiation source 11a. The intensity I of the first beam of radiation 21a at various positions of the receiving medium is schematically shown in FIG. 5B. The higher the intensity, the more energy is supplied to the ink. Part of the energy supplied by the first beam 21a is applied in the form of heat, which results in an increase in the temperature of the ink droplet 16. In FIG. 5B, the temperature of the ink at various positions of the receiving medium 2 is also shown schematically. At point A, the first beam 21 a first contacts the receiving medium 2. At this point, the intensity I of the first beam 21a is basically zero. Therefore, the temperature of the ink droplet 16 has not yet increased due to the radiation of the first beam 21a. At a further downstream position, the radiation intensity of the first beam 21a is higher. This consequently increases the speed of precuring. In addition, the temperature of the ink droplet 16 increases. As shown in FIG. 5B, at point B, the intensity of the radiation emitted by the first radiation source 11a, the temperature of the droplet is not adapted to reach T _1. Thus, at point B, the droplet 16 is still in an immobilized state and is partially cured in the precuring step. At point B, the second beam 22a begins to irradiate the droplet 16 applied on the receiving medium. The second beam as shown in FIG. 5A is a diverging beam. The second beam 22a is emitted by the second radiation source 11b. The radiation of the second beam 22a has a second dominant wavelength and a second intensity. By irradiating the droplet with the second beam of radiation 22a, the droplet is post-cured. As explained above, by post-curing the droplets, the ink droplets 16 are completely cured and the ink layer is solidified. When the ink is solidified, heating the ink layer above the temperature T ₁ can no longer affect the appearance, such as the gloss of the printed image. At a position on the receiving medium 2 downstream from point B, the ink may be irradiated by both a first beam 21a and a second beam 22a of radiation. Thus, when the ink droplet 16 is irradiated by the second beam of radiation 22a, the ink is post-cured. When post cure is performed, the ink can be heated to a temperature above T ₁ without adversely affecting the appearance of the print.

At a point downstream from point B, the ink may be irradiated by both the first beam of radiation 21a and the second beam of radiation 22a. When the post-curing of ink starts, the influence of the first beam 21a becomes relatively small. As shown in FIG. 5B, the intensity of the first beam 21a of radiation irradiating the receiving medium 2 is not constant and depends on the position on the receiving medium. Locally, the intensity of the first beam 21a of the radiation, the temperature of the ink is made to be higher than the locally T _1. However, this is only downstream of position B, ie where the post-curing process has already been started. Therefore, the local high intensity of the first beam of radiation 21a need not adversely affect the appearance of the print if the second beam of radiation 22a is properly positioned relative to the first beam of radiation 21a. .

  The second radiation source 11b as shown in FIG. 5A is in an inclined position. By tilting the radiation source, the area of the receiving medium 2 that is irradiated with the beam emitted by the radiation source can be controlled. One skilled in the art will appreciate that the position of the second radiation source 11b can be suitably selected to illuminate a selected area of the receiving medium 2.

  Detailed embodiments of the present invention are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be implemented in various forms. Accordingly, the specific structural and functional details disclosed herein are not intended to be limiting, but rather to variously employ the specification as a basis for claims and in a structure that is appropriately detailed in nature. Therefore, it should be construed as a representative standard in teaching to those skilled in the art. In particular, the features presented and described in the individual dependent claims may be applied in combination and any combination of such claims is thereby disclosed.

  Furthermore, the terms and phrases used herein are not intended to be limiting, but rather to provide an understandable description of the invention. As used herein, the term “a” or “an” is defined as one or more. As used herein, the term “plurality” is defined as two or more. As used herein, the term “another” is defined as at least a second or more. As used herein, the terms “comprising” and / or “having” are defined as comprising (ie, open words). As used herein, the term “coupled” does not necessarily appear directly, but is defined as a connection.

Claims (9)

A method of applying an image on a receiving medium,
a) a step for injecting droplets of ink jet printing UV curable phase change ink from the head onto a receiver medium hot, high temperature is a temperature higher than the phase transition temperatures T _1, the phase transition temperatures T _1, it A step that is the temperature at which the ink becomes immobilized when:
b) the droplets of the deposited ink comprising the steps of cooling to a temperature lower than T _1, ink droplets are thereby changed from a liquid state to a stationary state, the steps,
c) precuring the deposited ink droplets by irradiating the ink droplets with a first ultraviolet beam, wherein the first beam has a first intensity;
d) post-curing the deposited ink by irradiating the ink droplets with a second ultraviolet beam, the second beam having a second intensity;
With
Pre-curing is done before post-curing,
The intensity of the first beam, at least before the curing step, the temperature of ink is controlled so as not to exceed T _1, method.   The method of claim 1, wherein the first beam has a first dominant wavelength and the second beam has a second dominant wavelength.   The method of claim 2, wherein the first dominant wavelength is longer than the second dominant wavelength.   4. A method according to any one of claims 1 to 3, wherein the ink comprises a gelling material. The method according to claim 1, wherein the ink comprises a crystalline component and T ₁ is the melting temperature of the crystalline component.   6. The method according to claim 1, wherein in step a) the print head is reciprocated in the main scanning direction, the main scanning direction being substantially perpendicular to the paper transport direction.   In step c), the first UV beam is provided by the first UV source, the second UV beam is provided by the second UV source, and the first UV source and the second UV source are both synchronized with the main scan. The method of claim 6, wherein the method is moved in a direction. An inkjet printer for applying an image on a receiving medium,
An inkjet printhead configured to eject droplets of ultraviolet curable phase change ink;
A first UV source adapted to provide a first UV beam during operation;
A second UV source adapted to provide a second UV beam during operation;
Transport means for moving the recording medium in the paper transport direction relative to the inkjet print head and the first and second ultraviolet light sources;
With
An ink jet printer, wherein the second UV light source is positioned downstream relative to the ink jet print head and the first UV light source.   The ink jet printer according to claim 8, wherein the ink jet printer comprises a temperature adjusting means for adjusting the temperature of the receiving medium.

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